Lorentz National Park is a national park located in Papua, Indonesia, in the southwest of western New Guinea. With an area of 25,056 km2 (9,674 mi2), it is the largest national park in southeast Asia. In 1999 Lorentz was declared a World Heritage Site by UNESCO.

An outstanding example of the biodiversity of New Guinea, Lorentz is one of the most ecologically diverse national parks in the world. It is the only nature reserve in the Asia-Pacific region to contain a full altitudinal array of ecosystems ranging through marine areas, mangroves, tidal and freshwater swamp forest, lowland and montane rainforest, alpine tundra, and equatorial glaciers.

At 4884 meters, Puncak Jaya (formerly Carstensz Pyramid) is the tallest mountain between the Himalayas and the Andes.

Birdlife International has called Lorentz Park “probably the single most important reserve in New Guinea” It contains five of World Wildlife Fund's "Global 200" ecoregions: Southern New Guinea Lowland Forests; New Guinea Montane Forests; New Guinea Central Range Subalpine Grasslands; New Guinea Mangroves; and New Guinea Rivers and Streams.

Lorentz Park contains many unmapped and unexplored areas, and is certain to contain many species of plants and animals as yet unknown to Western science. Local communities' ethnobotanical and ethnozoological knowledge of the Lorentz biota is also very poorly documented.

The park is named for Hendrikus Albertus Lorentz, a Dutch explorer who passed through the area on his 1909–10 expedition.

Lorentz National Park has 630 documented species of bird (around 95% of the total number of bird species in Papua) and 123 mammalian species. Birds include two species of cassowary, 31 dove and pigeon species, and 60 species of kingfisher. Six bird species are endemic to the Snow Mountains including the Snow Mountain quail and Snow Mountains robin, 26 species are endemic to the Central Papuan Ranges while three are endemic to the South Papuan Lowlands. Threatened species include the southern cassowary, Alpine woolly rat, southern crowned pigeon, Pesquet's parrot, Salvadori's teal and Macgregor's giant honeyeater.

The mammal species include the long-beaked echidna, short-beaked echidna, and four species of cuscus as well as wallabies, quolls and tree-kangaroos.Endemic to the Sudirman Range is the dingiso, a tree-kangaroo species only discovered in 1995.

The area of the national park has been inhabited for more than 25,000 years. The forests of Lorentz encompass the traditional lands of eight indigenous ethnic groups, including the Asmat, Amung, Dani, Sempan, and Nduga. Estimates of the current population vary between 6,300 and 10,000.

It is widely acknowledged that conservation management strategies for the park will have to incorporate the needs and aspirations of these peoples if the park is to succeed in protecting biodiversity. Moreover, cultural diversity is another important measure of success for the park.

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